Gaskets are often used to provide a fluid type seal between two engaging, contronting, or mating parts. A common example includes pipes or similar conduit having machined flanges which are butted together over a gasket, the gasket having a large central opening matching that of the interior of the pipes as well as much smaller peripheral holes registering with like holes in the flanges jointly to receive bolts or the like to secure the assembly together. Another common example is that of a cylinder head gasket for internal combustion engines which is held under compression between a cylinder block and a cylinder head and insures against leakage of fluids like water.
In general, gasket materials comprise a base sheet of uniform thickness which may be of metal or of a fibrous composition, held together by a suitable bonding agent, and a deformable elastomer coat or bead which may cover all or only selected areas of the sheet. In use, the coat or bead deforms or spreads under pressure of forcing together the parts between which the gasket material lies and aids in realizing a desired fluid-type seal between the parts.
At present, gaskets designed to function at high temperatures are manufactured from two or three ply laminates consisting of one or two metal sheets and one to three asbestos sheets. However, these laminates are expensive to manufacture and require excessive labor and material. Also, the use of asbestos has become increasingly regarded as toxic and unsafe to handle.
Normally, high temperatue application makes severe demands on gaskets. Many gasketing materials are simply unable to meet such demands, and those which are tentatively able to do so have quite brief useful lives.
U.S. Pat. No. 2,605,194 to Smith describes preparation of a paint including a resin composed of siloxane structural units which is pigmented with powdered aluminum and air dried to a non-tacky state.
U.S. Pat. No. 3,505,099 and U.S. Pat. No. 3,560,244, both to Neuroth, disclose methods for bonding a curable silicone rubber or a polysiloxane to a substrate, characterized in that a zinc dust primer composition is first applied to the substrate. Subsequently, a silane or an organopolysiloxane is used to coat the primer composition after which a curable silicone rubber or an organopolysiloxane is applied.